The present invention relates in general to fiber optics technology and more particularly to a fiber optic transmission system with low cost transmitter compensation.
Inexpensive optical components, such as electro-absorption modulated lasers have several limitations that can affect optical signal transport. These limitations include a relatively low extinction rate, a low output power, and a relatively high chirp. A chirped signal effectively has a time varying change in its central wavelength over the duration of a pulse. This will produce a distortion as the corresponding frequency components at different points travel at different effective velocities. In light of these limitations, conventional optical communication systems have largely avoided the use of electro-absorption modulated lasers.
The present invention recognizes a need for a system and method operable to effectively and economically reduce distortion caused by low cost transmitters, such as electro-absorption modulators. In accordance with the present invention, a fiber optic transmission system with low cost transmitter compensation is provided that substantially eliminates or greatly reduces disadvantages and problems associated with conventional fiber optic systems.
According to one embodiment, a fiber optic transmission system with low cost transmitter compensation comprises an electro-absorption modulated laser operable to generate an optical signal for transmission over a fiber optic communication link. The system further comprises a Raman amplifier stage coupled to the communication link, the Raman amplifier stage having a gain medium including a dispersion compensating fiber. The dispersion compensating fiber is operable to at least partially compensate for a distortion caused by the electro-absorption modulated laser. The Raman amplifier stage is operable to at least partially compensate for a loss associated with the dispersion compensation fiber.
According to another embodiment, a fiber optic transmission system with low cost transmitter compensation comprises an electro-absorption modulated laser operable to generate an optical signal for transmission over a fiber optic communication link, and a Raman amplifier stage coupled to the communication link. The Raman amplifier stage comprises a gain medium having a negative sign of dispersion. The gain medium is operable to at least partially compensate for a chirp caused by the electro-absorption modulated laser, and the Raman amplifier stage is operable to at least partially compensate for a loss associated with the gain medium.
In yet another embodiment, a fiber optic transmission system with low cost transmitter compensation comprises a continuum source comprising a continuum source transmitter operable to generate an approximate spectral continuum and a signal splitter operable to separate the approximate spectral continuum into a plurality of wavelength signals for transmission over a fiber optic communication link. The system further comprises a Raman amplifier stage coupled to the communication link, the Raman amplifier stage having a gain medium including a dispersion compensating fiber. The dispersion compensating fiber is operable to at least partially compensate for a distortion caused by the continuum source, and wherein the Raman amplifier stage is operable to at least partially compensate for a loss associated with the dispersion compensation fiber.
In a method embodiment, a method for compensating low cost transmitter signal distortion comprises receiving from a communication link at a Raman amplification stage comprising a dispersion compensating fiber serving as at least a portion of a gain medium, an optical signal generated using an electro-absorption modulated laser. The optical signal has a distortion caused by the laser. The method further comprises performing dispersion compensation in the Raman amplification stage to at least partially compensate for the distortion caused by the electro-absorption modulated laser, and performing amplification in the Raman amplification stage to compensate for a loss introduced by the dispersion compensation.
In another method embodiment, a method for compensating low cost transmitter signal distortion comprises receiving from a communication link at a Raman amplification stage comprising a gain medium having a negative slope of dispersion, an optical signal generated using an electro-absorption modulated laser. The optical signal comprises a distortion caused by the laser. The method further comprises performing dispersion compensation in the Raman amplification stage using the gain medium to at least partially compensate for the distortion caused by the electro-absorption modulated laser, and performing amplification in the Raman amplification stage to compensate for a loss introduced by the dispersion compensation.
Numerous technical advantages are provided according to various embodiments of the present invention. Particular embodiments of the invention may exhibit none, some, or all of the following advantages depending on the implementation. For example, in one embodiment, signal distortion, such as chirp, is reduced or eliminated using a dispersion compensating element that is coupled to or part of the communication link. A Raman amplification stage at least partially compensates for losses induced to the system by the dispersion compensating element. In some cases, the Raman amplification stage may impart a net gain to the optical signal in the gain fiber.
In one particular embodiment, the dispersion compensating element can comprise a fiber having a negative slope of dispersion, which comprises all or a portion of a gain medium of the amplifier stage. In other embodiments, the dispersion compensating element could comprise a dispersion compensating fiber comprising all or a portion of a gain medium of the Raman amplifier stage. In either case, the dispersion compensating gain fiber can be pumped to provide gain sufficient to offset at least some losses of the dispersion compensating element. In some cases, the gain fiber can be pumped sufficiently to provide a net gain to the optical signal.
These techniques facilitate the use of relatively inexpensive components, such as EMLs, at relatively high bit rates (e.g., more than 9.5 gigabits per second), while maintaining acceptable system performance levels. Other technical advantages may be readily ascertainable by those skilled in the art from the following figures, description, and claims.